Highly flexible starch-based films

ABSTRACT

Film-forming compositions are disclosed that can comprise, on a dry solids basis, 25 to 75 percent by weight of certain starch derivatives and 25 to 75% primary external plasticizer. The starch derivatives can be chemically modified starches that range in molecular weight from 100,000 to 2,000,000. The high levels of plasticizer in the films give excellent film flexibility and integrity.

BACKGROUND OF THE INVENTION

This invention relates to starch compositions useful in forming flexiblefilms. More particularly, it relates to film-forming compositionscontaining starch in combination with certain plasticizers.

Gelatin is a protein that forms thermo-reversible films. Gel massescomposed of gelatin and a plasticizer such as glycerin are formulated tobe liquid above room temperature, form a film when cast on a cooledsurface, and re-melt when exposed to higher temperatures again. Thisability to re-tackify enables encapsulation of liquid materials ingelatin soft capsules. Films formed from plasticized gelatin set veryquickly and have high wet film strength. They are also very elastic withgood clarity. Plasticized gelatin also has a relatively low viscosity,even when used at high solids concentrations. In addition, when gelatinis in the presence of water at room temperature, it swells but does notgo into solution until heat is applied.

Although gelatin is useful in soft gel applications because of its rapidgelling ability, excellent film forming properties, and ability toimpart oxygen impermeability, it has the disadvantages of high cost,limited availability, non-kosher status for food products and, at times,batch property variations. Because of these shortcomings, thoseindustries where the need for gelatin is greatest have long sought meansfor replacing gelatin.

A number of food and industrial applications would benefit by aninexpensive and readily available structural material from a renewableresource, particularly one that is edible and/or biodegradable.Applications such as agricultural mulch, food packaging, and soft andhard gel capsules for cosmetics, pharmaceuticals and paintballs, need amaterial that is both strong and flexible under a range of useconditions. Applications such as adhesives, coatings, and caulkings donot have the rigorous strength requirements of free-standing films, butlack of brittleness can be just as important.

Starch meets many of the above requirements, and is an attractive rawmaterial for these applications. Its tendency to brittleness, however,has generally blocked its use in these areas.

There have been some previous reports of plasticized starch films.Lourdin (D. Lourdin, G. D. Valle, P. Colonna, Carbohydrate Polymers 27(1995) 261-270) incorporated up to 20% glycerol in starch films, butfound that their mechanical properties were far inferior to those ofsynthetic film formers. They found that increasing the amylose contentof the starch improved tensile strength. Arranitoyannis (CarbohydratePolymers 36 (1998) 105-119) measured moderately high tensile values onstarch films containing up to 25% polyhydric alcohols. When theplasticized films were oven dried to less than 6% moisture content, theybecame extremely brittle. Incorporating 15% hydroxypropyl units onto thestarch molecules improved film flexibility. Shih (F. F. Shih, in“Chemistry of Novel Foods”, A. M. Spanier, M. Tamura, H. Okai, 0. Mills,eds., Allured Pub. Corp., Carol Stream, Ill., Ch. 14, pp 179-186)reported tensile values on starch films containing up to 25%plasticizer, but reported that unplasticized films were too fragile forinstrumental analysis. In general, increasing plasticizer increases filmelongation while decreasing modulus and tensile strength. Other reportsof starch-based films include J. D. Christen, U.S. Pat. No. 4,026,986,1977; J. C. Rankin, I. A. Wolf, H. A. Davis, C. E. Rist, Industr. Engr.Chem. 3 (1958), 120-123; 1. A. Wolff, H. A. Davis, J. E. Cluskey, L. J.Gundrum, C. E. Rist, Industr. Eng Chem. 43 (1951) 915-919; A. M. Mark,W. B. Roth, C. L. Mehltretter, C. W. Rist, Food Technol. 20 (1966),75-77; W. B. Roth, C. L. Mehltretter, Food Technol. 21, (1967), 72-74;L. Jokay, G. E. Nelson, E. L. Powell, Food Technol. 21 (1967),1064-1066; and J. L. Willet, B. K. Jasberg, C. L Swanson in “Polymersfrom Agricultural Coproducts, eds. M. L. Fishman, R. G. Friedman and S.J. Huange, pp 50-68, Amer. Chem. Soc., Washington DC. These films arereported to be very sensitive to environmental humidity and tend toembrittle in low humidity environments.

Starch has also been included as a component in films containingproteins, such as gelatin, and carbohydrate-based hydrocolloids.Plasticizers are generally added to these systems as well. In most ofthese systems, starch is a secondary film former; the mechanicalproperties of the film reflect more strongly the properties of the otherpolymer(s) in the film. The following illustrates these types ofsystems. Laurent (L. Laurent, European Patent 0 547 551 Al, 1992),combines 5-40% starch with 5-40% gelatin and 10-40% plasticizer to makeflexible, edible films. Arvanitoyannis (I. Arvanitoyannis, E. Psomiadou,A. Nakayama; Carbohydrate Polymers 31, (1996) 179-192) developed ediblefilms containing starch and sodium caseinate with up to 30% sugar orglycerol. Arvanitoyannis (I. Arvanitoyannis, A. Nakayama, S. Aiba,Carbohydrate Polymers 36 (1998) 105-119) developed edible films composedof starch and gelatin with up to 25% polyol plasticizer. Psomiadou (E.Psomiadou, I. Arvanitoyannis, N. Yamamoto; Carbohydrate Polymers 31(1996) 193-204) studied films composed of starch, microcrystallinecellulose and methylcellulose containing up to 30% polyol plasticizers.

There is a long-standing need for improved film-forming compositionsthat do not have the shortcomings of prior art compositions.

SUMMARY OF THE INVENTION

One aspect of the present invention is a gelatin-free film-formingcomposition that comprises starch material and a primary externalplasticizer. The starch material is selected from the group consistingof modified starch and waxy starch, and has a dextrose equivalent (DE)of less than about 1, and preferably has no measurable DE (using theLane-Eynon method). The weight ratio of plasticizer to starch materialin the composition preferably is at least 0.5:1, more preferably is fromabout 0.5:1 to about 3:1, and most preferably is from about 1:1 to about3:1. This composition optionally may include, in addition to starch andplasticizer, gums, hydrocolloids, synthetic polymers, and/or otheradditives, but is preferably free of protein. “Gelatin-free” and“protein-free” are used herein to mean that no more than trace amounts(e.g., no more than about 0.1 weight percent) of the listed material ispresent in the composition.

The composition can be prepared with water, and preferably has a solidsconcentration of about 30-70%. (All composition percentages given hereinare by weight unless otherwise stated.) In one preferred embodiment ofthe invention, the solids in the composition comprise 25-50% starchmaterial and 50-75% plasticizer.

The starch material preferably comprises starch that has been chemicallymodified with a monoreactive moiety to a degree of substitution of atleast about 0.015. In a particularly preferred embodiment, the starchmaterial is selected from the group consisting of ether and esterderivatives of starch, such as hydroxypropyl, hydroxyethyl, succinate,and octenyl succinate starch. One specific embodiment of the inventioncomprises hydroxypropylated potato starch having a degree ofsubstitution of about 0.015-0.30 and a molecular weight of about200,000-2,000,000. Another specific embodiment of the inventioncomprises hydroxyethylated corn starch having a degree of substitutionof about 0.015-0.3 and a molecular weight of about 200,000-2,000,000.Another specific embodiment of the invention comprises hydroxypropylatedhigh-amylose corn starch with a degree of substitution of 0.015-0.3 anda molecular weight of about 200,000-2,000,000.

In some embodiments of the invention, one or more water soluble gums areadded to the mixture of starch and plasticizer. The gum is preferably0-15% of the total solids in the mixture. The gum preferably is selectedfrom the group consisting of carrageenan, locust bean, xanthan, gellan,agar, alginates, guar, gum arabic, and pectin. A combination of kappacarrageenan and iota carrageenan, most preferably in a weight ratio ofabout 1:1, is especially preferred.

In another embodiment of the invention, water soluble synthetic polymersmay be added to the starch and plasticizer mixture. The syntheticpolymer is preferably 0-50% of the total solids in the mixture. Thepreferred synthetic polymer is polyvinyl alcohol.

In another embodiment of the invention, organic or inorganic filler orpigment particles can be added. The pigments may be chosen from a listincluding clays, calcium carbonate, titanium dioxide, and syntheticorganic pigments.

Industrial plasticizers are discussed in the Encyclopedia of ChemicalTechnology, 4^(th) ed., Vol 19, pp 258-280, 1997. A plasticizer is asubstance which, when added to another material, increases the softnessand flexibility of that material. Without being bound by theory, it isbelieved that plasticizers increase flexibility of polymeric materialsby increasing the free volume within the material. Randomly distributedwithin the material and interspersed among the polymer chains, theplasticizer molecules interfere with the polymer's ability to align itschains and pack into ordered structures. Molecular ordering increasesthe density of the material (decreases free volume) and impedes mobilityof the polymer chains within the material. The increase in free volumeimparted by the plasticizer allows room for chain segments to move. Thematerial can then more readily accommodate an applied force bydeforming.

Polymers can be plasticized in two general ways: “internally” and“externally.” Internal plasticization can occur, for example, throughthe incorporation of a variety of chemical moieties along the starchmolecular chains through ether or ester linkages. These moieties includehydroxypropyl, hydroxyethyl, carboxymethyl, succinyl andoctenylsuccinyl, to name a few. An irregular array of substituents alongthe polymer backbone prevents close and regular chain packing, andincreases free volume in the material.

External plasticizers are relatively small molecules that are misciblewith the polymer, and impede chain alignment. External plasticizers areof two distinct classes: primary and secondary. Primary plasticizers areeffective in modifying the mechanical properties of the material ontheir own. Secondary plasticizers may be incompatible, or ineffective,at plasticizing the material on their own, but when added in combinationwith the primary plasticizer, can be very effective. They are sometimescalled “extenders.”

The plasticizers required in this invention are primary, externalplasticizers, such as sugars and low molecular weight polyols. Theproperties of the composition optionally can be further enhanced byusing internal and/or secondary external plasticizers. A suitablesecondary external plasticizer is water. The polyhydric alcohols arehygroscopic; their presence in the starch compositions increases thewater content relative to an un-plasticized starch.

Preferred plasticizers for use in the present invention have the generalformula C_(n)O_(n)H_(x), wherein n has a value between 3 and 6, and xhas a value between 2n and (2n+2), where at least 80% of the oxygen isin the form of hydroxyl groups, and the remaining are in the form ofether groups. This group of preferred plasticizers also includes dimers,disaccharides and low molecular weight (e.g., 300-1800 MW)oligosaccarides of these compounds, and may also include ether or esterderivatives of these compounds. Particular examples of suitableplasticizers include glycerol, diethylene glycol, sorbitol, sorbitolesters, maltitol, sucrose, fructose, invert sugars, corn syrup, andmixtures of one or more of these.

In preparing the films described in this invention, the mixture ofstarch and water is heated with stirring to hydrate fully all componentsin the mixture. The hydration of starch by heating is termed “cooking.”The preferred conditions for cooking the starch mixture are 80-200° C.for 5-60 minutes. Those versed in the art of starch cooking willrecognize that a variety of cooking techniques may be employed,including but not limited to, open kettles or high-pressure jet cookers.In another embodiment of the invention, instant, pre-gelled orcold-water swelling starches may be used. For these starches, it is notrequired that the mixture be heated to hydrate fully the starch.

The plasticizer, may be, but is not required to be, mixed with thestarch and water prior to cooking. The gum, synthetic polymer, or othercomponents of the film-forming mix, may be, but are not required to be,mixed with the starch and water prior to cooking. Whether or not thenon-starch components are mixed with the starch and water prior tocooking will depend on a number of considerations, including thehydration requirements of the other components, their thermal stability,viscosity constraints, and convenience.

Another aspect of the invention is a flexible adhesive for paper tapeand other paper-based articles comprised of the above-describedstarch-based composition, usually with much of the water removed. Yetanother aspect of the invention is a flexible paper coating comprised ofthe above-described composition. Yet another aspect of the invention isa flexible coating in which the starch-based composition is afilm-forming component, but which may also include fillers or pigments,latex emulsions or other additives.

Another aspect of the invention is an edible film that comprises theabove-described starch-based composition, usually with much of the waterremoved. Yet another aspect of the invention is a soft gel capsule thatcomprises a sealed capsule wall and a first substance that isencapsulated by the sealed capsule wall. The capsule wall comprises theabove-described starch-based composition. In one embodiment of theinvention, the film or the capsule wall consists essentially of thecombination of starch material and plasticizer.

The first substance encapsulated by the capsule wall can be any of avariety of materials that have been encapsulated by gelatin in the past.Many such substances are edible, including drugs, vitamins, nutritionalsupplements, and pre-measured food ingredients such as flavorings. Itcan also comprise, for example, photographic or dye solutions.

Another aspect of the invention is a method of encapsulating a firstsubstance. This method comprises the steps of providing a firstsubstance and an edible film as described above, and encapsulating thefirst substance in the film. Preferably, the film used in this methodhas been formed on a surface having a temperature of at least about 100°F.

In one preferred embodiment of the invention, the film or capsule wallconsists essentially of the combination of starch material, plasticizer,and optionally gum.

The present invention provides an economical alternative to thesynthetic polymers currently used to impart dimensional stability andbinding strength in adhesives and industrial coatings. It also providesan economical means for replacing gelatin in compositions utilized inthe production of soft gel for food, pharmaceutical, and industrialapplications. Further, the starch-based materials of this invention arecompatible with existing application equipment used for manufacture oftapes, coated papers, and various products that in the past have beenprimarily comprised of gelatin.

In compositions of the present invention, the starch, plasticizer, andany other solid ingredients preferably make up from about 30 to 70% byweight of an aqueous slurry. Flexible films are prepared by blendingtogether the starch, plasticizer, and water, and heating the mixture toa temperature and for a time sufficient to gelatinize the starch fully,(e.g., 80-200° C. for 5-60 min). Additional materials may be added tothe mixture of starch and plasticizer in order to impart improvedfunctionality. These materials may be added before or after heattreatment. The mixture is then sheeted, while warm or hot, to form athin film. The mixture may be sheeted directly onto paper, board orother surface when used as a coating or adhesive, or onto a castingsurface from which the cooled film can be lifted and transfer to rolls,or to fabrication equipment.

The present invention has a number of benefits. Starch is a low cost andreadily available material. The starch may be modified using a number ofchemical and physical means to enhance its properties while maintainingits status as a material approved as a food additive by the FDA. It maybe subjected to a number of additional modifications while maintainingits FDA acceptability for use in contact with foods. It isbiodegradable. It is water soluble and therefore does not requireexpensive, hazardous and/or volatile solvents that many other polymersrequire for processing. A range of materials are available forplasticizing starch which are both inexpensive and FDA approved for fooduse. In addition, the compositions of the present invention can becooked more easily than the high amylose compositions that have beenused in the past.

A film comprising the above-described composition can function as apressure sensitive adhesive. The combination of a high plasticizercontent and a highly substituted starch plasticizes the film to thepoint of providing tack through a broad humidity range.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Examples of modified starches that can be used in the present inventioninclude non-retrograding starches derived by chemical modification ofstarch from any plant source, including corn, waxy maize, potato, sweetpotato, wheat, rice, sago, tapioca, sorghum, high amylose corn, and thelike. The particular starch chosen will depend on its performance,availability, and cost. Among the useful modified starches are thecommon ether and ester derivatives of starch, including but not limitedto hydroxypropyl, hydroxyethyl, succinate, and octenyl succinate starchderivatives. Because waxy starches do not retrograde, they are suitablefor use without derivatization. Also included among the modifiedstarches suitable for use in the practice of this invention are thethermally converted, fluidity or thin boiling type products derived fromthe aforementioned types of chemically modified starches. Such materialsmay be of lower molecular weight, prepared by heating the modifiedstarch alone or by subjecting the starch to a hydrolytic acid and/orheat treatment, or by any other known method designed for the thermalconversion of the starch, such as enzymic heat treatment.

Preferred modified starches are the hydroxyethyl derivatives of dentcorn starch and the hydroxypropyl derivatives of potato starch, eachpreferably having a degree of substitution from 0.015-0.30 ds and amolecular weight of from 100,000 to 2,000,000. In the case of waxystarches of corn, potato, etc., the branches of the amylopectin replacethe function of the ether or ester substituents; these starches arefunctional in the present invention without additional chemicalmodification, although their properties are not impaired by additionalmodification, and are enhanced by molecular weight reduction.

Suitable plasticizers include, but are not limited to, glycerol,sorbitol, maltitol, fructose, sucrose, corn syrup, and mixtures thereof.

A variety of optional ingredients may be incorporated into the starchcompositions of this invention, before, during, or after cooking thestarch. Among the suitable materials that may be utilized are gums,synthetic polymers, preservatives, colorants, clays, pigments, flavoringagents, hardeners, antifoggers, sensitizers, and spreading agents. Theinclusion of such additives has no adverse effect upon the propertiesexhibited by the novel starch-based compositions of the presentinvention.

Suitable hydrocolloid gums include carrageenan, locust bean gum, xanthangum, gellan gum, agar, alginates, guar gum, gum arabic, cellulosicderivatives and pectin. Suitable synthetic polymer additives includepolyvinyl alcohol, polyethylene glycol, polyacrylamide and polyethyleneoxide, and certain derivatives of these polymers.

A composition of the present invention is formed by combining the drysolids (i.e., the modified starch or waxy starch, plasticizer, and anyother additives), slurrying in water, and heating at a temperature andfor a time sufficient to hydrate the starch, and other gums ifnecessary. Optionally, this can take place under a vacuum or highpressure. Films can be formed from these starch-based compositions byany conventional method designed to solubilize and deposit a continuouscoating or layer of the solution onto a substrate or mold of any form.Among the suitable coating techniques are spraying, dipping, air knife,trailing blade, reverse and direct roll coaters, etc. A film, such as anovercoating or capsule shell, may then be formed by drying the coatedsolution to a desired moisture content, using any means suitable for theparticular purpose. Suitable conventional means include heated rollers,warm or cold air impingement, low humidity chamber or oven drying, etc.For example, during paper coating, the coated sheet is passed oversteam-heated rolls to drive moisture from the coating.

EXAMPLES

The invention will be further illustrated by, but is not intended to belimited to, the following examples.

Compositions were prepared containing the component amounts given inExamples 1-3, on a dry basis. The relative starch molecular weight isreflected in the grams starch needed to give 1000 cps viscosity at 35°C., 160 rpm, using a Rapid Visco Analyzer (Model RVA-4D, Foss FoodTechnology, Eden Prairie, Minn.) (hereafter referred to as “RVA”). InExamples 1-3, the starch, fructose, and sufficient water to give totalsample weight of 1000 g, were mixed together in a beaker. The slurry wasthen cooked using a bench-top jet cooker at 260-270° F., 3.5 gal/minflow rate, and tail pipe residence time of 20 sec. The cooked starchpastes were collected in glass beakers, covered tightly with foil, andplaced in a 85° C. water bath until needed.

Example 1

230 g starch containing 2% hydroxyethyl substitution, acid hydrolyzed togive a viscosity of 1000 cps at 15% cooked paste solids

230 g crystalline fructose

sufficient water to give 1000 g slurry

Example 2

180 g starch containing 2% hydroxyethyl substitution, acid hydrolyzed togive a viscosity of 1000 cps at 10% cooked paste solids

270 g crystalline fructose

sufficient water to give 1000 g slurry

Example 3

150 g starch containing 2% hydroxyethyl substitution, acid hydrolyzed togive a viscosity of 1000 cps at 10% cooked paste solids

300 g crystalline fructose

sufficient water to give 1000 g slurry

Pre-weighed sheets of 23 lb/3000 ft² base paper were coated with thestarch pastes using a #10 draw-down rod, to give a coating pick-up of 16lb/3000 ft². A top sheet of 23 lb/3000 ft² paper was placed on top ofthe wet starch coating, and smoothed into place by drawing a drydraw-down rod over the top. The finished tapes were allowed to air dryovernight.

The tapes were cut into 7 mm×70 mm strips, and their tensile strengthsmeasured using a Stable Microsystems TA-XT2 Texture Analyze equippedwith jaw clamp attachments. Ten tests were run on each tape, in both themachine and cross directions, and the results averaged.

Table 1 summarizes the results. Included in the table are tests run ontape prepared from the same base paper and 16 lb/3000 ft² amorphouspolypropylene as the tape laminate. It can be seen that the starch-basedadhesives impart as much tensile strength to the tape while greatlyincreasing the extensibility of the tape. The control tapes are brittleand break at a very low elongation. With the plasticized starch, theextension to break is increased by as much as a factor of 3.

TABLE 1 Effect of plasticized starch laminate on tensile strength andplasticity of tape, compared with a standard amorphous polypropylenelaminate Extension Force to Starch: to Break Break, lbs/in Tape adhesivePlasticizer avg st dev avg st dev Machine Direction none-2x base paper —1.1% 0.2 55 3 amorphous polypropylene — 1.5% 0.2 57 3 Example 1 1:1 2.1%0.4 62 6 Example 2 1:1.5 2.5% 0.2 58 2 Example 3 1:2 2.1% 0.2 53 3 CrossDirection none-2x base paper — 3.1% 0.4 18 1 amorphous polypropylene —4.4% 1.2 22 2 Example 1 1:1 4.6% 1.4 21 2 Example 2 1:1.5 6.2% 1.0 21 2Example 3 1:2 6.1% 0.6 20 1

Examples 4-9 illustrate the effects of plasticizers, in their variousforms, on film flexibility. The plasticizer in these formulations isfructose. It is an external, primary plasticizer. Hydroxypropyl unitsadded to the starch molecular chains act as internal plasticizers.Fructose is hygroscopic, and, in high relative humidity, facilitates theuptake of moisture into the starch films. The water acts as a secondary,external plasticizer. The relative contributions of each can be seen bycomparing the flexibility rating of the films.

The compositions of Example films 4-9 are listed in Table 2. Allstarches had weight average molecular weights of 600,000. Starchmoistures ranged from 9-11%. To prepare the films, the starch,plasticizer and water were mixed together in the cup of an RVA, andheated, using 160 rpm stirring, to 98° C. over 4.5 minutes. The mixturewas held at 98° C., with continued stirring, for 6.5 minutes, thentransferred to a smooth surface and drawn into a film of 0.5 mmthickness using a draw-down bar. They were allowed to set, then agedovernight at the relative humidity conditions indicated in Table 2.Their relative flexibilities were then evaluated by bending the films.Films which shattered with little force were given a flexibility ratingof zero. Films which were flexible and pliant upon bending were given arating often. These results are given in Table 3.

TABLE 2 Compositions of Example Film Formulations Ex- am- % HP Starchfruc- Wa- slurry Plasti- ple on weight tose ter solids, cizer/ %Relative # Starch (g) (g) (g) % Starch Humidity 4 2 11.6 2.1 21.4 35 0.255 5 2 9.4 7.5 18.1 45 0.9 55 6 2 6.6 11.8 16.6 50 2 55 7 0 10.7 8.416.0 50 0.9 55 5 2 9.4 7.5 18.1 45 0.9 55 8 4.9 9.9 8.4 16.7 50 0.9 55 52 9.4 7.5 18.1 45 0.9 55 9 2 9.4 7.5 18.1 45 0.9 25

TABLE 3 Flexibility Ratings of Example Films Plasticizer/ % HP on %Relative Flexibility Film # Starch Starch Humidity rating 4 0.2 2 55 0 50.9 2 55 5 6 2 2 55 8 7 0.9 0 55 0 5 0.9 2 55 5 8 0.9 4.9 55 10 5 0.9 255 5 9 0.9 2 25 3

The film analyses of Table 3 are divided into 3 sections. The firstsection compares the effect of level of plasticizer. Aplasticizer/starch ratio of 0.2/1 yielded a very brittle films whichshattered with little force. Increasing plasticizer increasesflexibility. The second group of results in Table 3 compare the effectof hydroxypropyl substitution on starch. A surprising aspect of thisinvention is the large effect of starch substitution on filmflexibility. While the 4.9% HP groups on starch comprise only about 2.7%of film solids, they render a more flexible film than one containing 67%fructose plasticizer. The third section of Table 3 compares the effectof atmospheric humidity on film flexibility. The plasticizers of thisinvention are hygroscopic and draw moisture from the air into the film.This moisture acts as a secondary external plasticizer. It contributesto the effect of the primary plasticizer, increasing plasticization. Itshould be noted that conventional starch films containing 5-30%plasticizer are reported to be extremely sensitive to relative humidity.These films of this invention vary in flexibility with variations inhumidity, but remain flexible. They are not embrittled by lowatmospheric humidity.

Examples 10-16 illustrate the effect of film composition on theproperties of viscosity, rate of film formation and film strength.Compositions were prepared containing the component amounts given inExamples 10-16 on a dry solids basis.

Example 10

5.2 g potato starch, substituted with 3 wt % hydroxypropyl groups and of600,000 molecular weight

0.75 g kappa carrageenan

9.7 g Sorbitol Special (obtained from SPI Polyols, New Castle, Del.)

Example 11

8.4 g potato starch, substituted with 0.5% hydroxypropyl groups and of600,000 molecular weight

11.8 g Sorbitol Special

Example 12

8.4 g potato starch, substituted with 3.0% hydroxypropyl groups and of600,000 molecular weight

11.8 g Sorbitol Special

0.5 mm thickness.

Example 13

5.2 g potato starch, substituted with 3 wt % hydroxypropyl groups and of600,000 molecular weight

0.75 g gellan

9.7 g sorbitol

0.5 mm thickness.

Example 14

5.2 g waxy corn starch of 800,000 molecular weight

0.75 g kappa carrageenan

9.7 g sorbitol

Example 15

5.2 g potato starch, substituted with 3 wt % hydroxypropyl groups and of600,000 molecular weight

0.75 g kappa carrageenan

9.7 g glycerine

Example 16

5.2 g potato starch, substituted with 3 wt % hydroxypropyl groups and of600,000 molecular weight

0.75 g kappa carrageenan

9.7 g Sorbitol Special

Sufficient 1% NaCl to bring to 35 g total mass.

Starch molecular weights were measured by gel permeation chromatographyand weight averaged. Starch viscosities are measured using an RVA. InExamples 10-16, the starch, plasticizer, and gum, if used, were mixedwith sufficient deionized water (except where indicated) to give a totalslurry mass of 35 g. The components were mixed together in the cup ofthe RVA, and heated, using 160 rpm stirring, to 98° C. over 4.5 minutes.The mixture was held at 98° C., with continued stirring, for 6.5minutes, then transferred to a chilled surface and drawn into a film of0.5 mm thickness for film testing. A second paste of the samecomposition was cooked in the same way and then transferred into apre-heated glass jar, tightly capped, and placed into an oven for potlife evaluations.

In particular, in Examples 10-16, the film samples were prepared bycasting a layer of the test solution at about 180° F. (82° C.) onto aTeflon-coated piece of glass (approximately 9 in×13 in). The bottom ofthe glass was in contact with circulating cold water so that the surfacetemperature of the glass was 52° C. The film was formed by pouring thehot paste onto the Teflon surface and then quickly drawing the pasteacross the glass using a Bird Applicator or similar device, the gapwidth of which could be adjusted to control film thickness. Wet filmthicknesses were typically 0.5-0.8 mm. The films were cast, dried, andaged in a room controlled to 70° F. and 25-30% relative humidity.

The viscosity of the starch mixture was measured by the RVA instrument,which records viscosity throughout the cook.

Pot life was evaluated by transferring the hot paste into preheatedglass jars with screw lids, and placing these in a 180° F. oven. Thefluidity of the mass was evaluated after 2 hours by tipping the jarsupside down and assigning a flow rating of 0-5. A mass that flowed withthe ease of water was given a rating of 5; a mass which did not flow atall was given a rating of 0. The oven temperature was then lowered by10° F. and the samples allowed to equilibrate for 2 hours, and thentheir flow properties re-assessed. The oven was lowered in 10° F.increments until all samples had a flow rating of zero—that is, they hadall gelled.

Thermo-reversibility was assessed by reheating the pot life samples,described above, in 10° F. increments, allowing them to equilibrate ateach temperature, and then assigning a flow rating using the samecriteria as for pot life.

The films were evaluated for rate of filming using a Gardco ElectronicMulticycle Circular Drying Time Recorder, and following test methodprocedure ASTM D 5895. The recorder was placed above the wet film, and astylus was lowered onto the surface of the film and allowed to rotatefor a defined time of 10 minutes. Three points were determined from thistest: tack free, dry hard, and dry through. Tack free is defined as thepoint in the path made by the stylus on the film where the continuoustrack ends and a discontinuous track or tear begins. Dry hard is thepoint in the path where the stylus no longer tears the film, and onlyleaves a visible trace. Dry through is reached when the stylus no longerleaves any visible track on the film.

The tensile strength of the wet film was measured using a StableMicrosystems TA-XT2 Texture Analyzer. To do this, 0.5 in×8 in stripswere cut from the wet film 5 minutes after it was cast and these wereloaded onto the Texture Analyzer. The tensile test was started 15minutes after the film was cast.

Film appearance (color and clarity) was evaluated on the basis of visualobservation.

The physical properties of the hot starch/plasticizer pastes forExamples 10-16, and the resulting films, are listed below in Table 4.

TABLE 4 Peak Wet film Exam- viscosity Hot paste Time Time tensile Potlife Minimum Re- ple during final visc, until tack until dry strength,rating @ flowable softening number cook, cps cps, 98° C. free, sec hard,sec g force 180° F. temp, ° F. temp, ° F. 10 18000 1700 <5 <10 75 3.5160 150 11 14000 2500 65 100 * 12 13000 1150 4020  5700  * 13 2300 <5<10 108  0.5 >180  >180  14 13000 2400 <5 <10 65 3.0 170 150 15 160001500 <5 <10 50 4.0 160 150 16 11000 1300 <5 <10 75 3.5 170 150 * Tooweak to test

Example 17 describes a pressure sensitive adhesive composed of highlysubstitued starch and high level of plasticizer. The components ofExample 17 were mixed together, cooked as described for Examples 1-3,and the film cast onto a glass surface.

Example 17

6.92 g potato starch, 600,000 mol wt, 4.85% hydroxypropyl content, 7.34%moisture

12.96 g glycerine

15.11 g water

The film of Example 17 remains tacky for months at humidities rangingfrom 25% to 55% RH. Paper can be stuck to the adhesive, removed from it,and re-stuck to it without damage to the paper or loss of adhesive tack.

The preceding description of specific embodiments of the presentinvention is not intended to be a complete list of every possibleembodiment of the invention. Persons skilled in this field willrecognize that modifications can be made to the specific embodimentsdescribed here that would be within the scope of the present invention.

What is claimed is:
 1. A gelatin-free film-forming composition,comprising: starch material having an average molecular weight of about100,000-2,000,000 and a dextrose equivalent less than about 1 andselected from the group consisting of (a) starch which has beenchemically modified with a monoreactive moiety to a degree ofsubstitution of at least about 0.015 and is selected from the groupconsisting of ether and ester derivatives of starch and (b) waxy starch;and a primary external plasticizer; wherein the weight ratio ofplasticizer to starch material is at least about 0.5:1.
 2. Thecomposition of claim 1, wherein the weight ratio of plasticizer tostarch material is from about 0.5:1 to about 3:1.
 3. The composition ofclaim 2, wherein the weight ratio of plasticizer to starch material isfrom about 1:1 to about 3:1.
 4. The composition of claim 1, wherein thecomposition is protein-free.
 5. The composition of claim 1, furthercomprising water.
 6. The composition of claim 5, wherein the compositioncomprises 30-70% by weight dry solids.
 7. The composition of claim 6,wherein the dry solids consist essentially of starch material andplasticizer.
 8. The composition of claim 6, wherein the dry solids inthe composition comprise 25-75% starch material, 25-75% plasticizer, and0-15% gum or synthetic polymer.
 9. The composition of claim 8, whereinthe composition comprises at least one gum selected from the groupconsisting of carrageenan, locust bean, xanthan, gellan, agar,alginates, guar, gum arabic, cellulosic and pectin.
 10. The compositionof claim 8, wherein the composition comprises at least one syntheticpolymer selected from the group consisting of polyvinyl alcohol,polyethylene glycol, polyacrylamide, polyethylene oxide, and derivativesor mixtures thereof.
 11. The composition of claim 1 wherein the starchmaterial is selected from the group consisting of hydroxypropyl,hydroxyethyl, succinate, and octenyl succinate starch.
 12. Thecomposition of claim 1, wherein the starch material comprises waxystarch.
 13. The composition of claim 1, wherein the starch materialcomprises hydroxypropylated potato starch having a degree ofsubstitution of about 0.015-0.30 and a molecular weight of about100,000-2,000,000.
 14. The composition of claim 1, wherein the starchmaterial comprises hydroxyethylated dent corn starch having a degree ofsubstitution of about 0.015-0.30 and a molecular weight of about100,000-2,000,000.
 15. The composition of claim 1, wherein theplasticizer comprises at least one polyol.
 16. The composition of claim1, wherein the plasticizer comprised at least one compound having theformula C_(n)O_(n)H_(x), wherein n has a value between 3 and 6, and xhas a value between 2n and (2n+2), or a dimer or oligomer of such acompounds.
 17. The composition of claim 1, wherein the plasticizer isselected from the group consisting of glycerol, sorbitol, maltitol,fructose, sucrose, corn syrup, and mixtures thereof.
 18. A filmcomprising the composition of any of claims 1-17.
 19. The film of claim18, wherein the film consists essentially of the composition.
 20. Thefilm of claim 18, wherein the film is coated on paper.
 21. The film ofclaim 18, wherein the film has pressure sensitive adhesive properties.